The present invention relates to the art of image reconstruction. It finds particular application in conjunction with reconstructing x-ray transmission data from computed tomography (CT) scanners which move a cone-beam or wedge beam of radiation along a helical trajectory, and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in conjunction with the reconstruction of data from CT scanners, nuclear cameras, and other diagnostic scanners that process data representing nonparallel trajectories.
Conventionally, spiral or helical CT scanners include an x-ray source which projects a thin slice or beam of penetrating radiation. The x-ray source is mounted for rotational movement about a subject that is translated along the axis of rotation. An arc or ring of radiation detectors receive radiation which has traversed the subject. Data from the radiation detectors represents a single spiraling slice through the subject. The data from the detectors is reconstructed into a three-dimensional image representation.
Current helical CT scanners with two or three detector rings improve data acquisition speed and permit thin slab scanning. Several 3-D image reconstruction techniques for reconstructing data from helical cone or wedge beam systems have been suggested. For example, commonly assigned U.S. Pat. No. 5,625,660 to Tuy discloses an image reconstruction technique for helical partial cone-beam data in which the data stream is divided into two parts which are processed separately and then recombined. In addition, other similar reconstruction techniques process a single data stream. These three-dimensional reconstruction techniques generally involve increased computational load and complexity. This is due to the fact that these reconstruction techniques perform xe2x80x9ctrue 3D reconstruction,xe2x80x9d involving a 3D backprojection of convolved projections.
In contrast, current 2D helical reconstruction techniques enjoy decreased computational load and simplicity. However, current 2D helical reconstruction techniques limit the number of rings or cone angle over which accurate reconstructions can be obtained. An additional difficulty with reconstruction of spiral cone or wedge beam data is the elimination of redundant rays of data.
The present invention contemplates a new and improved image reconstruction technique which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a method of volumetric image reconstruction includes collecting partial cone beam data in two-dimensional arrays at a plurality of sampling positions, where the collected data corresponds to rays of radiation which diverge in two dimensions from a common vertex as the vertex travels along a continuous path. A plurality of two-dimensional oblique surfaces are defined throughout a region of interest and rays of radiation which pass through the plurality of oblique surfaces are defined. The data from the identified rays is reconstructed into a reconstruction cylinder having an axis along a z-direction. A volume data set is generated from the reconstructed oblique surface data.
In accordance with another aspect of the present invention, a method of diagnostic imaging includes generating penetrating radiation and the receiving the penetrating radiation with two-dimensional radiation detectors along a plurality of divergent rays, where the rays are focused at a common origin vertex and diverge in two dimensions. The vertex is rotated along at least an arc segment of a helical path. The radiation detectors are sampled at a plurality of angular increments along the helical arc segment to generate a plurality of two-dimensional projection views, where each view includes a two-dimensional array of data values and each data value corresponds to one of the divergent rays. A first and last oblique surface are defined, where the first and last oblique surfaces are formed by the intersection of a cone beam of penetrating radiation and the region of interest. A plurality of additional oblique surfaces are defined, where the plurality of oblique surfaces are at least one of rotated and translated with respect to the first oblique surface. Projection views corresponding to each oblique surface are weighed and a two-dimensional convolution of the projection view data is computed. The convolved projection data corresponding to each oblique surface is two-dimensionally backprojected into a volumetric image memory.
In accordance with another aspect of the present invention, a method of selecting non-redundant rays of penetrating radiation during a computed tomography scan is provided where the non-redundant rays from a plurality of oblique surfaces for two-dimensional reconstruction into a volumetric image representation. The method includes at each angular orientation about an examination region, selecting detected rays of penetrating radiation that intersect a geometric center point of each oblique surface. The method further comprises interatively identifying rays of penetrating radiation which are tangent to surface rings extending outward from the geometric center point of each oblique surface.
In accordance with a more limited aspect of the present invention, the method includes where penetrating radiation data does not exist, interpolating closest adjacent rays tangent to the oblique surface rings between the center point and an outer radius of the region of interest.
In accordance with another aspect of the present invention, a computed tomography scanner includes a first gantry which defines an examination region and a rotating gantry mounted to the first gantry for rotation about the examination region. A source of penetrating radiation is arranged on the rotating gantry for rotation therewith. The source of penetrating radiation emit a cone-shaped beam of radiation that passes through the examination region as the rotating gantry rotates. A subject support holds a subject being examined at least partially within the examination region, wherein at least one of the first gantry and the subject support is translated such that the subject passes through the examination region while the rotating gantry is rotated and the source of penetrating radiation follows a helical path relative to the subject. A two dimensional array of radiation detectors is arranged to receive the radiation emitted from the source of penetrating radiation after it has traversed the examination region. A reconstruction processor reconstructs images of the subject from data collected by the two-dimensional array of radiation detectors. The reconstruction processor includes a control processor which defines a plurality of oblique surfaces, where the oblique surfaces are defined by the intersection of the cone-shaped beam of radiation and a portion of the subject, and an interpolator which identifies non-redundant rays of penetrating radiation that pass through the oblique surfaces. A first data processor weights the data corresponding to the identified non-redundant rays and a second data processor receives data from the first data processor and performs a two-dimensional convolution on the data. A backprojector receives the data from the second data processor and two-dimensionally backprojects it into an image memory. The CT scanner further includes a human-viewable display which accessed an image memory to display to display reconstructed images of the subject.
One advantage of the present invention is increased efficiency in both the scan and reconstruction process.
Another advantage of the present invention is that it provides accurate reconstruction for larger area cone beam projections.
Another advantage of the present invention is that it enjoys greater computational simplicity.
Yet another advantage of the present invention resides in the ability to achieve a three-dimensional volumetric reconstruction using conventional two-dimensional reconstruction techniques.
Other benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.